Field of the Invention
The present invention relates to a front sheet fixing structure for a front sheet to be attached to surfaces of a display device and control panel of a controller for controlling an industrial apparatus, such as a machine tool.
Description of the Related Art
A front sheet for protecting a touch panel, key switches, etc., from dust, oil, and water is attached to surfaces of a display screen and control panel. FIG. 6 shows a fixing structure configured to secure a front sheet 12 directly to a molded housing 10 using a double-sided adhesive tape.
As shown in FIG. 6, the front sheet 12 is affixed to the molded housing 10 with the double-sided adhesive tape so that it covers the entire operation surface of the housing 10. The front sheet consists mainly of a resin sheet (e.g., polyethylene terephthalate (PET) sheet) and is very low in rigidity. If the front sheet 12 is affixed directly to the molded housing 10, therefore, it may be wrinkled or deformed due to a difference in thermal expansion coefficient between the molded housing 10 and the front sheet 12, in case of change in temperature of the installation environment.
Japanese Patent Application Laid-Open No. 2007-293488 discloses an arrangement in which a metal frame is integrally molded with a resin bezel and the front sheet 12 is affixed to the metal frame so that it cannot be wrinkled or deformed.
Due to the difference in thermal expansion coefficient between the molded housing 10 and the front sheet 12 and the recent trend toward larger-screen displays, the front sheet 12 is liable to be wrinkled or deformed as a result of temperature change. In the aforementioned technique in which a metal frame is integrally molded with a resin bezel and a front sheet is affixed to the metal frame, processes of production are more complicated and costly than in a technique in which a front sheet of a simple resin molded product is affixed directly to a molded housing. Since the front sheet is flat, moreover, the design of the operation surface of a display device or control panel is inevitably flat, lacking three-dimensional distinction, if the entire operation surface is covered by the front sheet.